Functional comparisons between isoforms of the sarcoplasmic or endoplasmic reticulum family of calcium pumps

• Published in: The Journal of biological chemistry 1992-07, Vol.267 (20), p.14483-14489
• Main Authors: LYTTON, J, WESTLIN, M, BURK, S. E, SHULL, G. E, MACLENNAN, D. H
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; calcium; Calcium - metabolism; Calcium - pharmacology; Calcium-Transporting ATPases - genetics; Calcium-Transporting ATPases - metabolism; Cell Line; endoplasmic reticulum; Endoplasmic Reticulum - enzymology; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Gene Expression; Hydrolases; Isoenzymes - genetics; Isoenzymes - metabolism; Kinetics; Mathematics; Phosphorylation; pumps; sarcoplasmic reticulum; Sarcoplasmic Reticulum - enzymology; Transfection; Vanadates - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)49738-x

ATP-dependent calcium pumps that reside in intracellular organelles are encoded by a family of structurally related enzymes, termed the sarcoplasmic or endoplasmic reticulum Ca(2+)-ATPases (SERCA), which each have a distinct pattern of tissue-specific and developmentally regulated expression. A COS-1 cell expression system was used to examine the biochemical properties of the isoforms: SERCA1 (fast-twitch skeletal muscle). SERCA2a (cardiac/slow-twitch skeletal muscle), SERCA2b (ubiquitous smooth- and non-muscle), and SERCA3 (non-muscle). Each isoform was expressed efficiently and appeared to be targeted to the endoplasmic reticulum. All isoforms displayed qualitatively similar enzymatic properties and were activated by calcium in a cooperative manner with a Hill coefficient of 2. The quantitative properties of SERCA1 and SERCA2a (the muscle isoforms) were identical in all respects. SERCA2b, however, appeared to have a lower turnover rate for both calcium transport and ATP hydrolysis. SERCA3 displayed a reduced apparent affinity for calcium, an increased apparent affinity for vanadate, and an altered pH dependence when compared with the other isoforms. These properties are consistent with an enzyme in which the equilibrium between the E1 and E2 conformations is shifted toward the E2 state.